The present invention relates to a positioning device for a document processing device, more particularly, for positioning a processing device, such as a printer head, an image reading device and so on, with respect to a platen roller.
As a printing device for a facsimile, a printer and so on, a thermal head or an LED (Light Emitting Diode) head has been used. In case letters or characters are printed onto a heat sensitive paper by a thermal head, the heat sensitive paper must be pushed onto a heating section of the thermal head by a platen roller, or the heating section is pushed onto the platen roller through the heat sensitive paper. In this case, it is required to precisely position the center of the platen roller to the heating section of the thermal head.
For this purpose, as shown in FIGS. 1 and 2, a guide plate with a U-shape guide groove for a platen roller had been generally used, and attached to a support plate for constituting a heat radiating plate of the thermal head by means of screws. As shown in FIG. 1, a guide plate 1 is provided with a hole 1a, a positioning projection 1b, a supporting portion 1c, a fixing projection 1d, and a guide portion 1e for a platen roller 10. A support plate 2 for constituting a heat radiating plate for a thermal head includes screw holes 2a, and positioning holes 2b. The support plate 2 also includes a ceramic plate 7, a head plate 6 having a heating member 3, leading electrodes and so on, and a printed wiring board 12. When the support plate 2 and the guide plate 1 are connected, the positioning projection 1b is located in the positioning hole 2b, and a screw 5 is applied into the screw hole 2a through the hole 1a.
When the guide plate 1 with the support plate 2 is installed, the supporting portion 1c is located in a hole of a frame 13, and the fixing projection 1d is placed behind an edge of the frame 13. Springs 8 fixed on the frame urge the support plate 2, so that the guide plate 1 abuts against the edge of the frame 13. The platen roller 10 includes a shaft 10a, and bearing members 11 are mounted on projecting portions of the shaft 10a. The platen roller 10 is rotationally supported on an arm (not shown), and is inserted into the guide portions 1e such that the bearing members 11 are placed in the guide portions 1e of the guide plates 1. The platen roller 10 is moved in the guide portions 1e by the arm when necessary.
In the above structure, the support plate 2 requires a secondary processing for forming the screw holes 2a. Also, when the guide plates 1 are fixed to the support plate 2, the guide plates 1 must be precisely positioned on the support plate 2 and fixed thereto by the screws 5. Thus, the assembly work is not so efficient. Further, since the guide plates 1 are fixed to the back of the support plate 2, the thermal head is thickened to thereby enlarge the machine, which is opposite to the idea of making a compact machine.
In view of the above, thermal heads as shown in FIGS. 3 and 4 were proposed. A support plate 2A includes fixing holes 2e at longitudinal ends thereof, and guide plates 4 are attached to the plate 2A. Each guide plate 4 includes a guide portion 4a, a supporting portion 4c, a fixing projection 4d, and an inserting portion 4f with an engaging member 4b. When the plate 4 is fixed to the support plate 2A, the inserting portion 4f is inserted into the fixing hole 2e.
in FIG. 4, a support plate 2B includes fixing grooves 2g, 2h, and a guide plate 4' includes two inserting portions 4g, 4h with engaging members 4e, wherein the inserting portions 4g, 4h are inserted into the fixing grooves 2g, 2h to fix the guide plate 4' with the support plate 2B.
The above thermal heads can reduce the thickness, but since the guide plates for the platen rollers are laminated and fixed to the support plate, the thickness of the thermal head increases as well. Thus, the above structures do not necessarily reduce the thickness.
In a thermal head as shown in FIG. 5, a guide plate 1' includes a hole 1a' and a positioning projection 1b' as in the guide plate 1, and further includes a shaft hole 1c'. A support plate 2C includes screw holes 2a and positioning holes 2b. Two guide plates 1' are fixed to the support plate 2C, wherein each positioning projection 1b' is located in the positioning hole 2b, and the screw 5 is threaded into the screw hole 2a. Thereafter, the thermal head with the guide plates 1' is placed between side portions of a frame (not shown), and a shaft is inserted into holes of the side portions of the frame through the shaft holes 1c' to thereby fix the thermal head with the guide plates 1' to the frame. A platen roller 10 is rotationally fixed to the frame, as well. The shaft passing through the holes 1c' is positioned such that a printing head on the thermal head precisely aligns the platen roller 10. Thus, the shaft operates to align the position of the thermal head to the platen roller and to support the thermal head when the thermal head is pushed toward the platen roller for printing.
In the above structure, the guide plates 1' are fixed to the support plate 2C by the screws 5. Thus, additional processing is required for the support plate 2C, and also, the screws 5 and the flanges for the holes 1c' project from the thermal head to thereby increase the thickness of the thermal head. Therefore, the thermal head of FIG. 5 can not be made compact, as in the prior art shown in FIGS. 1-4.
Accordingly, the present invention has been made to obviate the drawbacks in the conventional processing device, such as thermal heads, and has an object to provide a positioning device for a document processing device, such as a printer head, an image reading device and so on, wherein the processing device can be easily and precisely positioned relative to a platen roller.
Another object of the invention is to provide a positioning device as stated above, wherein a processing for a support plate required for positioning the processing device to the platen roller is minimized.
A further object of the invention is to provide a positioning device as stated above, wherein the processing device can be made simple and compact.
A still further object of the invention is to provide a positioning device as stated above, which can be manufactured easily and economically.